I know there are already got one CEGUI wrapper inside crystal space ,but it's too "fat " for my small project,I've done some small GUI librarys inside Irrlicht,and Ogre ,But that's not API independent,so I was wondering if there is one small GUI library for crystal space or should I directly write one through crystal space 2D function,Do i have other options? what crystal core used for create gui stuff?

Nope, for pure-CS (not using CEL) projects, there's no alternative to CEGUI,not counting old AWS and AWS2 which are not maintained anymore(but one can find them in CSExtra repository).You could write your own with CS-only code, using csPixmap, for example.

CEL projects, like Crystal Core, generally use the "billboard" propclass.And, there's the python-widget set in $CEL/data/library/blpython/widgets/which Interstate Outlaws uses. There are now examples for it yet, apart studyingInterstate Outlaws or Ecksdee code.And it's somehow broken with trunk/1.9 at the moment (but works with 1.4 & 1.2.1).